Cannabis, also known as hemp, is a genus of hardy, dioecious, annual herbs. It has been used by humans throughout recorded history for its fiber, for its psychological and physiological effects as a drug, and for the nourishment and oil of its seeds.

The tough fiber of the plant, cultivated as hemp, has numerous textile uses. Its seed, chiefly used as caged-bird feed, is a valuable source of protein, energy, and long-chain fatty acids, and also contain oil that can be used to make paints, varnishes, and soaps. Most concentrated in the resin in the buds of the female plant, mildly psychedelic and other psychoactive and physiologically active chemical compounds known as cannabinoids are consumed for recreational, medicinal, and spiritual purposes. When so purposed, preparations of buds and leaves, sometimes called marijuana, and preparations derived from resinous extract, sometimes called hashish, are today usually consumed by inhaling vapor released by smoking or other heating, or by oral ingestion. Historically, tinctures, teas, and ointments were also common preparations.

Cannabis reproduces sexually. The flowers of the female plant, in cannabis usually called buds, are arranged in racemes and can produce hundreds of seeds. Males reach sexual maturity several weeks prior to females. Although genetics disposes a plant to become male, environmental factors, including the diurnal light cycle, can alter the sex. Natural hermaphrodites, with both male and female parts, are usually sterile but artificially induced hermaphrodites can have fully functional reproductive organs. 'Feminized' seed sold by many commercial seed suppliers are derived from artificially hermaphrodytic females that lack the male gene or by treating the seeds with hormones.

Cannabis uses C4 photosynthesis, which is not dependent upon a night cycle for carbon dioxide absorption. A cannabis plant in the vegetative growth phase of its life cycle can thrive under twenty-four hour daylight conditions, although some growers advocate a small rest period to avoid overstressing the plant. Flowering usually occurs when darkness exceeds eleven hours per day and can take up to six weeks.

In soil, the optimum pH for the plant is 5.8 to 6.5. In hydroponic growing, the nutrient solution is best at 5.5 to 6.1, making cannabis well-suited to hydroponics because this pH range is hostile to most bacteria and fungi.

Broadly, there are three groups of cannabis varieties that are cultivated today:

* Varieties primarily cultivated for their fibre, characterized by long stems and little branching.
* Varieties grown for seed from which hemp oil is extracted.
* Varieties grown for medicinal or recreational purposes. A nominal if not legal distinction is often made between hemp, with concentrations of psychoactive compounds far too low to be useful for that purpose, and marijuana.

The family Cannabaceae was formerly placed with the nettles in the order Urticales, but is now considered to be in the order Rosales. There is phylogenetic controversy as to whether the cultivated varieties of the plant are of a single species (Cannabis sativa) or represent distinct species (such as those called Cannabis indica, Cannabis ruderalis, or Cannabis americana). That there are different strains of cannabis has not been in question; whether these strains possess qualities of a true species or lesser taxonomic designations, such as races, ecotypes, cultivates, chemovars, and so on, has been at issue (Schultes and Hofmann 1980). Current research indicates the classification consists of more than one species. Botanists such as Richard E. Schultes at Harvard University and Loran C. Anderson at Florida State University conclude sufficient scientific evidence exists to support three species of cannabis: Cannabis sativa, Cannabis indica, and Cannabis ruderalis. C. sativa grows to a height of 18 feet (6 metres), is loosely branched, and thrives in cool, damp climates. C. indica grows from 3.5 to 4 feet (1.3 metres), is conical in shape, and thrives in hot, dry climates. C. ruderalis grows from 1 to 2.5 feet (0.4 to 0.7 m), is dense and never branches, and is found primarily in Russia. There are other distinguishing features as well, related to cell and leaf structures. There are gelatinous fibers in the wood and vessels that exist singly or in small groups in C. sativa. C. indica has liberiform fibers in its wood and its vessels occur in large groups. C. ruderalis is mostly intermediate in these characteristics. Although the number of leaflets may vary within a species, C. sativa normally has seven leaflets, C. indica has nine , and C. ruderalis has three. The leaflet of C. sativa is narrow, or lanceolate. The C. indica leaflet is broad, or oblanceolate. And the C. ruderalis leaflet is oval, or elliptic, being broadest at the mid-length of the leaf (Anderson 1974, 1980). All three species contain THC; C.indica produces the most and C. ruderalis the least. Cannabis has been cultivated for thousands of years for its intoxicating flowering tops and leaves, its fibrous stems and branches, and its nutritious seeds. A strain that is high in one of these three qualities tends to be low in the other two. C. indica, for example, is very low in fiber content but generates the most potent marijuana. C. sativa produces the hemp fibers that have been used for centuries for making rope and coarse woven produces, but races of C. sativa high in this quality contain very little THC (less than 0.5 percent). The seeds of C. sativa can also be harvested for use as animal feed and for producing oil that is used in cooking and in making paint.

Though the main psychoactive chemical compound in cannabis is ?9-tetrahydrocannabinol (THC), the plant is known to contain about sixty cannabinoids, including two others of particularly high concentration, cannabinol (CBN) and cannabidiol (CBD). CBD is a precursor to THC, and CBN is a product of the degradation of THC by exposure to oxygen. Differences in the chemical composition of cannabis varieties can produce substantially different effects in humans. Synthetic THC, called dronabinol, does not contain CBD, CBN, or other cannabinoids, which is one reason why its effects can differ significantly from those of of cannabis preparations.

Although the potency of most cannabis varieties is uncertain, most commonly available cannabis contains below 8% THC. Selective breeding and modern cultivation techniques like hydroponics have produced varieties with more than 25% THC. With varieties containing below 2% THC, such as those specifically cultivated for use as hemp, smoking may produce lightheadedness or mild headache but not inebriation. The THC content is also affected by the sex of the plant, with female plants generating substantially more resin than their male counterparts. Seedless varieties derived from unpollinated female plants have high THC content and are traditionally known as sinsemilla (Spanish: "without seed").

Smoking may pose the greatest risk to physical health, but may be reduced by using water pipes. Ingesting cannabis or vaporizing the cannabinoids from the plant are other safer methods of consumption.

THC has an effect on the modulation of the immune system which may have an effect on malignant cells, but there is insufficient scientific study to determine whether this might promote or limit cancer. Cannabinoid receptors are also present in the human reproductive system, but there is insufficient scientific study to conclusively determine the effects of cannabis on reproduction. Mild allergies to cannabis may be possible in some members of the population.

No fatal overdose due to cannabis use has ever been recorded in humans. According to the Merck Index, 12th edition, the LD50, the lethal dose for 50% of tested rats, was 42 milligrams per kilogram of body weight with forced inhalation. As for oral consumption, the LD50 for rats was 1270 mg/kg and 730 mg/kg for males and females, respectively. It would be impossible for THC in blood plasma to reach such a level in human cannabis smokers. Only with intravenous administration, a method rarely or never used by humans, may such a level be possible. Also, some evidence suggests that toxic levels may be higher for humans than for rats.

There is little conclusive scientific evidence about the long-term effects of human cannabis consumption. Many old studies which purported to demonstrate such effects were deeply flawed, with strong bias and poor methodology. The most significant confounding factor in determining long-term effects is the use of other drugs by test subjects in studies of cannabis use. When subjects who use only cannabis are combined in the same sample with subjects who use other drugs, an experiment could not conclude that its findings are indicative of an effect of the use of cannabis rather than an effect of the use of other drugs, or an effect of a complex combination of cannabis with other drugs.

Although it may become habitual, the use of cannabis does not result in physical dependence. Yet, with abstinence after heavy, chronic use, some tolerance may persist for several days and anxiousness, irritability and diminished appetite may occur. Also more vivid, memorable dreams (REM rebound) are common in heavy users who temporarily abstain.However, because cannabis is a peculiar psychedelic that is unlike typical depressant or stimulant drugs, these persistent effects are unlike those normally associated with physical dependence.

In some people cannabis use appears to cause significant medium-term decreases in cognitive performance, but performance on general intelligence and cognitive tests returns to "normal" within weeks of abstinence, depending on the level of use. However, subtle impairment of complex cognitive function may persist even after long periods of abstinence in some of the users who suffered from decresed cognitive performance in the first place

There is a correlation between cannabis use and psychosis, schizophrenia, and clinical depression in some people, but there is no evidence that cannabis use causes these illnesses. Rather, cannabis may trigger latent conditions or be part of a complex coordination of causes. Also, the physiological effects of cannabis as well as the subjective evidence of some users indicate the likelihood of people with depression using cannabis to alleviate such it's symptoms.

More scientific study is necessary to determine the long-term physiological effects of smoking cannabis. Because of the evolution of toxic chemicals, including carcinogens, during combustion, cannabis smoke may be unhealthy in a similar way that tobacco and other smoke is. In addition, many cannabis smokers inhale the smoke deeper into their lungs than do tobacco smokers, hold the inhalation for a greater length of time, and typically do so without a filter. However, the average cannabis user generally smokes far less than the average tobacco user. Also, cannabis smoke is free of nicotine, a carcinogen, and does not contain certain impurities and radioactivity that are present in most tobacco products. No studies have demonstrated a correlation between cannabis use and lung cancer.

Medically, cannabis is most often used as an appetite stimulant and pain reliever for certain terminal illnesses such as cancer and AIDS. It is also used to relieve glaucoma and certain neurological illnesses such as epilepsy and bipolar disorder. The medical use of cannabis is politically controversial, but it is sometimes recommended informally by physicians.

Cannabis has a long history of spiritual use, especially in India, where it has been used by wandering spiritual aspirants for centuries. The most famous religious group to use cannabis in a spiritual context are the Rastafarians, though they are by no means the only group. Many individuals also consider their use of cannabis to be spiritual regardless of organized religion.

Cannabis is prepared for human consumption to several forms:

* Flowering tops of female plants, called bud or buds.
* Concentrated resin, called hashish when prepared into a solid and hash oil when as an extracted oil. It is usually processed into blocks. It is called charas when it is pressed into long, thin rectangular pieces.
* Fine crystals of cannabinoids, called kif. It is produced by sifting buds for concentrated consumption or in order to produce hashish.
* Minimally potent leaves and detritus, called shake.

The most common method of cannabis consumption is by smoking a hit through one of several classes of devices:

1. By rolling it up, usually manually, into a cigarette, often called a joint, with thin rolling papers, or into a cigar, often called a blunt, with papers obtained by removing the tobacco from a standard cigar. In such preparation, tobacco or other smokeable material are sometimes combined into a single roll.
2. By using a pipe, often called a bowl, usually made of blown glass or sometimes metal. Blown-glass pipes are usually intricately and colorfully designed, with colors becoming more vivid after repeated use. Such pipes usually have a rush or carb hole which is covered by a finger for suction when beginning smoking, which is released to finish inhalation without advancing the burning any further. Tobacco pipes, pipes home-made by the user, and others, are also sometimes used.
3. In a water-pipe, or bong, by which the smoke is filtered through water so that it is cooler and may be more healthy. In such devices, the cannabis is placed into a bowl, which may be removable, and smoke is sucked through a body of water into a large chamber which is cleared by inhaling further after the rush hole is uncovered or the pipe-like part is removed. A hookah is a similar, water-filtering device with a long, flexible tube which the user may hold, through which the smoke passes before entering the mouth. Hookahs often have several tubes so that multiple users may smoke at the same time.
4. More rarely, a gravity bong, usually home-made, consists of a large water-filled bucket and a funnel, such as a milk jug or soft-drink bottle, with an open-ended or cut-out bottom and a bowl that can be sealed into the top when capped. The uncapped funnel is lowered into the water-filled bucket and then capped with the bowl of cannabis. The cannabis is then lit while slowly raising the funnel from the bucket, so that there is a negative air pressure in the funnel by which gas and smoke is pulled through the bowl. The raising of the now-smoke-filled funnel is stopped before the funnel is fully removed from the water, the cap is removed, and the user inhales from the top while carefully pushing the funnel back into the water. The volume of a smoke with this method is less easily controlled and can be hazardous.

Cannabis may be orally consumed by blending it with alcohol or fats. With this method, more cannabis must be used and the effects of the drug take longer to begin, but last longer and can be more physical rather than mental. It is also more difficult for one to regulate the dose. Common preparations involve blending with butter that is used in preparing brownies or cookies. Infusion in drinks containing milk and flavoring herbs is also possible, and more common in India.

The seeds of the plant, high in protein, energy, and fatty acids, can also be eaten and roasted. They contain little THC.

Usually with a vaporizer, cannabis can be heated to a temperature at which the active ingredients are released into gaseous form with little or no burning of the plant material. With this method, the user does not inhale the toxic chemicals that are byproducts of combustion and so is far more healthy.

The meaning of each of these terms may vary by region and context:

Cannabis: bud, brown frown (low quality), cess, cheeba, chronic (high quality), dagga (from Afrikaans via South Africa), dak, dank, dope, doobage, doja, draw, dro (derived from hydroponics), electric puha (from puha, a plant in New Zealand), frodis (from The Monkees), funk, ganja (from Hindi), grass, green, hash, hay, herb, indo, instaga, IZM, kind, leaf, Mary Jane, mids (middle quality), nugget, nug, pakalolo (from Hawai'ian), pot, reefer, regs (regular strength), sensi, shake (small quantity), skunk, shwag (low quality), sticky-icky-icky, tea, tree, wacky tobacky, weed

Cigarette: beedie, bifta, blunt (cigar papers), breezie, doobie, cannon (large), fatty, J, joint, L (cigar papers), muggle, reefer, spliff, gotti (cigar emptied of tobacco and filled without cutting), zoot

Reefer was common in the early twentieth century, but it is now often used only humorously, often in reference to the 1930s propaganda film Reefer Madness, which significantly misrepresented the effects of cannabis.

Intoxication: baked, blasted, blazed, buzzed, chink-eyed (offensive), faded, goofed, high, keyed, lit, mashed, monged, mullered, ripped, spaced (out), stoned, throwed

To smoke: bake, blaze, burn, cheef, chong, Choof, light up, puff, sesh (from session), toke (up)

Early twentieth century: mez, muggles, gage, viper jive.

Potent strains: White widow (light green-white in appearance), Buddha, 5-way (often said to be 5 strains genetically combined into 1), C99, AK-47 (C. sativa/C. indica cross), Bubblegum, mango buds (both very sticky), JuicyFruit, Orange Bud and Blueberry (plant smells or tastes somewhat like its name); G-13 (A mythical, primarily indica phenotype); BC Bud (from British Columbia, Canada); Afghani, Thunderfuck, White Kookamunga, Northern-lights (these two natives of northern provinces), Silver or Purple Haze, kush, Hydro, Thai or Thai stick (the legitimate product is C. sativa from Thailand or US Grown of Thai seed, the buds being long and treelike in appearance, often with string wrapped in a spiral pattern for the purpose of holding the bud together); Maui Wowie (from Hawai'i); Acapulco Gold. The term Thai stick is also used for imitation marijuana.

The use of cannabis, for food, fibers, and medicine, is thought to go back at least five millennia. Neolithic archaeological sites in China include cannabis seeds and plants. The first known mention of cannabis is in a Chinese medical text of 2737 BC. It was used as medicine throughout Asia and the Middle East to treat a variety of conditions. In India particularly, some sects of Hinduism associated cannabis with Shiva.

Cannabis was well known to the Scythians. Germans grew hemp for its fibers to make nautical ropes and material for clothes since ancient times. Large fields of hemp along the banks of the Rhine are featured in 19th century copper etchings.

American pioneers depended on hemp for clothes, canvas, rope, oil, food, and many other things. The plant was so important that Thomas Jefferson, as governor of Virginia, required every farmer in the state to plant hemp for the good of the economy and citizens' survival. In 1791, the cotton gin was invented and cotton began to replace hemp for clothing in the U.S. Cannabis was used medicinally in the western world (usually as a tincture) around the middle of the 19th century. It was famously used to treat Queen Victoria's menstrual pains, and was available from shops in the US. By the end of the 19th century its medicinal use began to fall as other drugs such as aspirin took over.

Until 1937, consumption and sale of marijuana was legal in most American states. In some areas it could be openly purchased in bulk from grocers or in cigarette form at newstands, though an increasing number of states had begun to outlaw it. In that year, federal law made possession or transfer of marijuana (without the purchase of a by-then incriminating tax stamp) illegal throughout the United States. This was contrary to the advice of the American Medical Association at the time. Legal opinions of time held that the federal government could not outlaw it entirely. The tax was $100 per pound of hemp, even for clothes or rope. The expense, extremely high for that time, was such that people stopped buying and making it.

The decision of the U.S. Congress was based in part on testimony derived from articles in the newspapers owned by William Randolph Hearst, who was heavily interested in DuPont Inc. Some analysts theorize DuPont wanted to boost declining post-war textile sales, and wished to eliminate hemp fiber as competition. Many argue that this seems unlikely given DuPont's lack of concern with the legal status of cotton, wool, and linen; although it should be noted that hemp's textile potential had not yet been largely exploited, while textile factories already had made large investments in equipment to handle cotton, wool, and linen. Others argue that Dupont wanted to eliminate cannabis because its high natural cellulose content made it a viable alternative to the company's developing innovation: modern plastic. Still, others could argue that hemp could never truly compete with the high strength and elasticity of synthetics, such as nylon.

Even more inflammatory and biased were the accusations by that period's US 'drug czar' Henry (Harry) Anslinger. Anslinger charged that the drug provoked murderous rampages in previously solid citizens. Anslinger testified that cannabis "makes darkies feel equal to white men," a complaint typical of much of the racist anti-drug rhetoric of the time, which for example emphasised opium's role in promoting Anglo-Chinese miscegenation. He told the married men in the audience: "Gentlemen, it will make your wives want to have sex with a Black man!" Anslinger also popularized the word marihuana for the plant, using a Mexican derived word (believed to be derived from a Brazilian Portuguese term for inebriation) in order to associate the plant with increasing numbers of Mexican immigrants, creating a negative stereotype which persists to this day.

The 1937 federal marijuana tax act was struck down by the Supreme Court in 1969. In a case brought by Timothy Leary, the Court held that the law's requirement that a possessor of marijuana present the substance before receiving the stamp, thereby placing the possessor in violation of the law against unlicensed possession, violated the Fifth Amendment privilege against self-incrimination. In 1970, the Controlled Substances Act made possession of marijuana illegal again, without the constitutional issues that scuttled the 1937 act.

Although cannabis has been used recreationally throughout its history, it first became well known in the United States during the jazz music scene of the late 1920s and 30s. Louis Armstrong became one of its most prominent and life-long devotees. Cannabis use was also a prominent part of 1960s counterculture.

Since the twentieth century, most legal jurisdictions of the world have laws against the use, possession, or transfer of cannabis, but there are many regions where certain circumstances of cannabis handling are legal and others where laws against its use, possession, or sale are not enforced. Many jurisdictions have also decriminalized possession of small quantities of cannabis, so that it is punished with a fine rather than imprisonment. Increasingly, many jurisdictions also permit cannabis use for medicinal purposes.

Acute effects of cannabis consumption vary according to the dose, the variety of the plant, the method of use, the individual, and the environment, but for the general population usually include some of the following:

* General change in consciousness
* Mild euphoria, feelings of general well-being
* Relaxation or stress reduction
* Enhanced recollection of episodic memory
* Physical pleasure
* Increased awareness of sensation
* Drowsiness, lassitude
* Disruption of linear memory
* Slowness, caution
* Paranoia, agitation, and anxiety
* Precipitation or exacerbation of latent or existing mental disorders
* Subjective potentiation of other drugs
* Pain relief (especially headaches and cramps)
* Increased appetite (colloquially known as "the munchies")
* Reduced nausea
* Dilation of alveoli (air sacs) in lungs
* Dilation of blood vessels (vasodilation), resulting in:
* Increased blood flow
* Reddening of the conjunctivae (red eye)
* Dry mouth (xerostomia)
* Headache
* Dizziness, confusion
* Lower intra-ocular pressure (within the eyeball)
* Lower blood pressure
* Increased metabolism of glucose, reducing blood sugar levels